This invention relates to medical devices, and more specifically, to human body implantable drug delivery pumps.
Briefly, the brain, not the point of an injury, registers any sensation of pain. When pain is felt, it is a reaction to signals that are transmitted throughout the body. These signals are sent from the pain source, through the nerves in the spinal cord, to the brain, where they are perceived as pain. Pain can be controlled by preventing the pain signals from reaching the brain.
The origin of some pain is neuropathic, while other pain is nociceptive. Neuropathic pain is pain that is caused by damage to nerve tissue. Nociceptive pain means pain caused by an injury or disease outside the nervous system.
Acute pain (such as spraining an ankle) acts as a warning to signal harm or possible damage to tissues in the body. It prevents additional damage by alerting you to react and remove the source of pain. However, when pain lasts a long time (over six months) and is not relieved by standard medical management, it is called xe2x80x9cchronicxe2x80x9d pain. In chronic pain, the pain signal no longer helps, but hinders the body. Pain is recognized as a major public health problem. In the United States, it is estimated that chronic pain affects 15% to 33% of the U.S. population, or as many as 70 million people. In fact, chronic pain disables more people than cancer or heart disease and costs the American people more than both combined. Pain costs an estimated $70 billion a year in medical costs, lost working days, and workers"" compensation.
APT(trademark) Neurostimulation (xe2x80x9cAdvanced Pain Therapy Neurostimulationxe2x80x9d) is available from Medtronic, Inc., and commonly used for neuropathic pain. APT(trademark) Intrathecal treatment, also available from Medtronic, Inc., is commonly used for nociceptive pain.
APT(trademark) Neurostimulation (including both spinal cord stimulation and peripheral nerve stimulation) uses a small neurostimulation system that is surgically placed under the skin to send mild electrical impulses to the spinal cord. The electrical impulses are delivered through a lead (a special medical wire) that is also surgically placed. These electrical impulses block the signal of pain from reaching the brain. Peripheral nerve stimulation works in the same way, but the lead is placed on the specific nerve that is causing pain rather than the spinal cord.
APT(trademark) Intrathecal uses a small pump that is surgically placed under the skin of the abdomen to deliver medication directly into the intrathecal space (where fluid flows around the spinal cord). The medication is delivered through a small tube called a catheter that is also surgically placed. The spinal cord is like a highway for pain signals on their way to the brain, where the feeling of pain is experienced by the body. Because the medication goes directly to the site of action in the spinal cord, where pain signals travel, APT(trademark) Intrathecal offers many people significant pain control with much lower doses of medication than would be required by oral medications (pills). This helps minimize the side effects that often accompany other treatments.
A doctor can do a screening test to see if APT(trademark) Intrathecal will relieve pain, before the patient commits to the therapy. In addition, APT(trademark) Intrathecal is non-destructive and reversible. Typically, people who have success with APT(trademark) Intrathecal experience greater than 50% reduction in their pain and improved ability to go about activities of daily living.
The SynchroMed(copyright) Infusion System is a fully implantable, programmable APT(trademark) Intrathecal system available from Medtronic. The SynchroMed(copyright) Infusion System has two parts that are both placed in the body during a surgical procedure: the catheter and the pump. The catheter is a small, soft tube. One end is connected to the catheter port of the pump, and the other end is placed in the intrathecal space (where fluid flows around the spinal cord). The pump is a round metal device that stores and releases prescribed amounts of medication directly into the intrathecal space. It is about one inch (2.5 cm) thick, three inches (8.5 cm) in diameter, and weighs about six ounces (205 g). It is made of titanium, a lightweight, medical-grade metal. The reservoir is the space inside the pump that holds the medication. The fill port is a raised center portion of the pump through which the pump is refilled. The doctor or a nurse inserts a needle through the patient""s skin and through the fill port to fill the pump. Some pumps have a side catheter access port that allows the doctor to inject other medications or sterile solutions directly into the catheter, bypassing the pump.
The SynchroMed(copyright) pump automatically delivers a controlled amount of medication through the catheter to the intrathecal space around the spinal cord, where it is most effective. The exact dosage, rate and timing prescribed by the doctor are entered in the pump using a programmer, an external computer-like device that controls the pump""s memory. Information about the patient""s prescription is stored in the pump""s memory. The doctor can easily review this information by using the programmer. The programmer communicates with the pump by radio signals that allow the doctor to tell how the pump is operating at any given time. The doctor also can use the programmer to change your medication dosage.
As indicated, an APT(trademark) Intrathecal pump is a sophisticated electromechanical device. In addition to its reservoir, fill port, and other mechanical components, the device includes microelectronics in an electronic chamber. Implantation of an APT(trademark) Intrathecal pump is also a significant life event. Given the electronics in the units and the significance of implantation, long-term excellence in the performance of the units is highly desirable. Unfortunately, one common failure mode (way things fail) for implantable device electronics is corrosion of conduction pathways, or short circuiting of the pathways, caused by the presence of water vapor and salts. The short circuiting of the pathways often occurs from dendrites which form between circuits which are at different voltage potentials, when in the presence of ionic vapors. Plastic components in the electronics (e.g., chip carriers), absorb trace amounts of water vapor in normal air, and these vapors can leave the plastics after implantation, risking corrosion.
Consistently, the electronics of the devices are protected. They are protected against liquids, and against humidity. Liquid protection, by surrounding the electronics in a hermetic enclosure, prevents entry of fluids from the human body or drugs from the drug pathway. Humidity protection provides for a dry environment for the internal electronic components. A dry interior promotes long life and accuracy in the performance of the electronic components.
In current device manufacture, a last or near-last step of manufacture is the humidity protection step. The device is fully assembled, with only a pinhole called a xe2x80x9ctigxe2x80x9d hole remaining as an opening to the interior. The unit is then xe2x80x9cbakedxe2x80x9d by bringing it to a temperature of about 100 degrees Fahrenheit (37 degrees C.) while a vacuum is created in the heating chamber or xe2x80x9covenxe2x80x9d. The air inside the unit is pulled by the vacuum through the tig hole, bringing internal moisture, including moisture previously absorbed in plastic components, out with it. Typically, the tig hole is so small that the time necessary to pull the air from the unit is a day to two days. The external vacuum is then reduced and in a short time, the baked unit is xe2x80x9cbackfilledxe2x80x9d with helium, meaning the vacuum inside the unit is filled with helium, also through the tig hole. Within the short time available, the tig hole is then welded closed.
This vacuum bake time can be a significant time constraint for assembling the implantable pump.
A primary object of the invention is to substantially advance the construction of human body implantable drug delivery pumps.
Another primary object is to substantially advance the manufacturing methods employed for manufacturing such pumps.
Another primary object is to minimize the consumption of time required by the current technique for humidity protection, and the complication of the rigors of time, temperature, vacuum, and location of its use.
Another primary object is to imbue the human body implantable drug delivery pump with structure eliminative of the current technique for humidity protection; that is, to provide a construction of the unit that permits assembly without use of the current technique for humidity protection.
Another object is to imbue the pump with structure that allows the reduction of a hermetic barrier between the electronics area and the motor area; that is, to provide a construction that works with a hermetic seal of the electronics area and motor area together, assuming the motor system has an impermeable barrier tubing that contains the drug being delivered.
Other primary objects include providing a pump structure eliminative and potentially eliminative of the unit baking and its use and complication, eliminative and potentially eliminative of the vacuum creation and its use and complication, and eliminative and potentially eliminative of the tig hole and its use and complication.
In a first aspect, then, the invention includes an improvement in a human body implantable drug delivery pump that comprises a housing including at least a first shield and a second shield. The housing defines an interior within the shields. The pump further includes a fluid reservoir within the housing, a fluid conduit also within the housing from the reservoir, an outlet from the fluid conduit to the exterior of the housing, and a pump member in the housing adapted to move fluid through the fluid conduit to the outlet. The fluid in the reservoir and fluid conduit is isolated from the pump interior. The pump further comprises a desiccant in the pump interior, the desiccant absorbent of moisture in the pump interior, and preferably absorbent of substantially all the moisture in the pump interior.
In another principal aspect, the invention is directed specifically to improvement in a human body implantable drug delivery pump of the type described in which the desiccant has a moisture absorbent property dependent on temperature, being lessened at higher temperatures, the desiccant being pre-heated to improve its moisture absorbent property before being placed in the pump. The desiccant is also further absorbent of moisture, whereby the desiccant may be placed within the housing during final assembly of the pump when the pump housing is not completely sealed, and the desiccant is absorbent during a time period of final assembly, and remains absorbent of substantially all the moisture within the housing after complete sealing of the housing. Most preferably, the desiccant is molded to fit free space within the housing, and the desiccant comprises a mixture of liquid silicon rubber and aluminum oxide.
These and other objects, aspects and advantages of the invention and its preferred embodiments are best understood by a complete reading of the detailed description of the preferred embodiment of the invention, which follows a brief description of the accompanying drawing.